1. Field of the Invention
The present invention relates to a laser ray transmitting colored thermoplastic resin composition containing a dis-azo salt forming dye and a method of laser welding.
2. Description of the Prior Art
Laser welding of synthetic resin materials can, for example, be conducted as described below. As shown in FIG. 1, one member incorporating a laser ray transmitting material and another member incorporating a laser ray absorbing material are brought into contact with each other. When an irradiating laser ray is passed from the laser ray transmitting material side to the laser ray absorbing material, the laser ray that has passed through the laser ray transmitting material is absorbed in the laser ray absorbing material and generates heat. By this heat, the laser ray absorbing material is made molten around the portion that has absorbed the laser ray, and the laser ray transmitting material is also made molten, the resins of the two members fuse together, and upon cooling sufficient welding strength is obtained and the laser ray transmitting material and the laser ray absorbing material are joined firmly. Features of laser welding include the capability of welding without bringing the laser ray generation portion in contact with the portion to be welded, the minimal thermal effect on the surrounding portion because the heating is localized, freedom from the problem of mechanical vibration, the capability of welding of fine portions and structures, high reproducibility, maintenance of high air-tightness, high welding strength, inconspicuous welded portion, and no generation of dust, etc.
Traditionally, resin parts have been joined together by clamping with clamping parts (bolts, screws, clips, etc.), adhesion using adhesives, vibration welding, ultrasonic welding, etc. According to laser welding, secure welding is achieved by simple operation to provide strength equivalent to or more than expected by conventional welding, and in addition labor saving, productivity improvements, production cost reductions, etc. can be achieved because vibration and heat have minimal effects. With these features, laser welding is suitable for the joining of functional components, electronic components, etc., for which the avoidance of the influence of vibration and heat is desired in, for example, the automobile industry, electric/electronic industry and other fields, and is applicable to the joining of resin parts of complex shapes.
As a technology concerning laser welding, Japanese Patent Laid-Open No. HEI-11-170371 [Patent Document 1] describes a method of laser welding comprising a process wherein a laser ray is irradiated so that it focuses on a portion where an opaque member comprising a laser ray absorbing thermoplastic synthetic resin and a colorless transparent member comprising a laser ray transmitting thermoplastic synthetic resin are in contact with each other. In this case, however, when viewed from the colorless transparent member side, the welded portion differs from the non-welded portion in color and smoothness, posing a problem of poor appearance.
Additionally, Japanese Patent Laid-Open No. 2000-266928 [Patent Document 2] and Japanese Patent Laid-Open No. 2002-060644 [Patent Document 3] employs dis-azo dyes as color filter colorants. However, these dis-azo dyes are faulty in that their dyes are relatively liable to sublimation. Therefore, during their blending in synthetic resins (engineering plastics, in particular, which require high temperatures for molding), coloring and molding, it is likely that dye decomposition products are produced and cause discoloration and physical property reductions. Additionally, their anti-migration quality and chemical resistance are insufficient and they lack practical applicability for resin compositions for molding, such as engineering plastics.    [Patent Document 1] Japanese Patent Laid-Open No. HEI-11-170371    [Patent Document 2] Japanese Patent Laid-Open No. 2000-266928    [Patent Document 3] Japanese Patent Laid-Open No. 2002-060644
The present invention has been developed in view of the aforementioned problems in the prior art, and is intended to provide a laser ray transmitting colored thermoplastic resin composition and a method of laser welding that do not pose color fading of the colored thermoplastic synthetic resin member in the heat treatment process prior to laser welding of the resin member and permit laser welding with substantially no dye sublimation.